1. Field of Invention
The present invention relates generally to cathodo-luminescent display devices and more particularly to a driving method for field emission electron emitters.
2. Background of the Invention
Cathodoluminescent field emission display devices are well known in the art and are commonly referred to as FEDs as disclosed in U.S. Pat. No. 5,313,140 (Smith, et al.), U.S. Pat. No. 5,387,844 (Browning), and U.S. Pat. No. 5,283,500 (Kochanski). Other display devices such as electroluminescent displays disclosed by U.S. Pat. No. 5,384,517 (Uno) and Liquid Crystal Displays are well known alternatives to the FED.
As is disclosed in U.S. Pat. No. 5,300,862 (issued Apr. 5, 1994 to N. Parker and J. Jaskie, for "Row Activating Method for FED Cathodoluminescent Display Assembly". incorporated herein by reference)
FIG. 1 is a partial perspective view representation of an image display device 100 as configured in accordance with the present invention. A supporting substrate 101 has disposed thereon a first group of conductive paths 102. An insulator layer 103 having a plurality of apertures 106 formed there through is deposited on supporting substrate 101 and on the plurality of conductive paths 102. Apertures 106 have disposed therein electron emitters 105 which electron emitters 105 further disposed on conductive paths 102 A second group of conductive paths 104 is disposed on insulating layer 103 and substantially peripherally about apertures 106. An anode 110, a viewing screen 107 having disposed thereon a cathodoluminescent material 108, is distally disposed with respect to electron emitters 105. An optional conductive layer 109 is disposed on the cathodoluminescent material (phosphor) 108, as shown, or layer 108 may be positioned between the viewing screen 107 and the phosphor 108.
Each conductive path of the first group of conductive paths 102 is operably coupled to electron emitters 105 which are disposed thereon. So formed, electron emitters 105 associated with a conductive path of the first group of conductive paths 102 may be selectively enabled to emit electrons by providing and electron source operably connected to the conductive path.
Each conductive path of the second group of conductive paths 104 is disposed peripherally about selected aperture 106 in which electron emitters 105 are disposed. So formed, electron emitters 105 associated with a conductive path of the second group of conductive paths 104 is induced to emit electrons provided that the conductive path of the second group of conductive paths 104 is operably connected to a voltage source (not shown) to enable the emission from the associated electron emitters 105 and the conductive path of the first group of conductive paths 102 to which electron emitters 105 are coupled is operably connected to an electron source (not shown).
Each aperture 106 together with the electron emitter 105 disposed therein and a conductive path of the first group of the plurality of conductive paths 102 on which the electron emitter 105 is disposed and to which the electron emitter 105 is operably coupled and an extraction electrode, including a conductive path of the second group of conductive paths 104 peripherally disposed there about, comprises a field emission device (FED). While the structure of FIG. 1 depicts an array of four FEDs, it should be understood that arrays of FEDs may comprise many millions of FEDs.
Selectively applying voltage to an extraction electrode of an FED and selectively operably connecting an electron source to a conductive path operably coupled to electron emitter 105 of the FED will result in electrons being emitted into a region between electron emitter 105 and distally disposed anode 110. Electrons emitted into this region traverse the region to strike anode 110 provided a voltage (not shown) is applied to anode 110. Each FED or, as desired, group of FEDs or the array of FEDs provides electrons to a determinate portion of phosphor 108. Such a determined portion of phosphor 108 is termed a picture element (pixel) and is the smallest area of the viewing screen which can be selectively controlled."
As also disclosed in the '862 patent and shown in FIG. 2 (FIG. 3 of '862 patent) "is a schematic representation of an image display 300 employing an array of FEDs wherein extraction electrodes 304B correspond to a first group of conductive paths and emitter conductive paths 304A correspond to a second group of conductive paths. In this embodiment, first and second groups of conductive paths 304B and 304A, respectively, make up a plurality of conductive paths. Appropriately energized, as described previously with reference to FEDs of FIG. 1, the FEDs selectively emit electrons. In the schematic depiction of FIG. 2 controlled current source 301A-301D is operably connected between each of the second group of conductive paths 304A and a reference potential, such as ground, to provide a determinate source of electrons to electron emitters 305 operably connected thereto. Each extraction electrode 304B is operably coupled to one output terminal of a plurality of output terminals 316 of switching circuit 302. A voltage source 303 is operably connected between an input terminal 311 of switching circuit 302 and a reference potential, such as ground.
By selectively controlling the desired level of electrons provided by controlled constant current sources 301A-301D and by selectively switching voltage source 303 to a selected output terminal of the plurality of output terminals 316 a row of FEDs is simultaneously energized and the electron emission from each FED of the row is determined. By providing that switching circuit 302 connects voltage source 303 to a single extraction electrode in a single row of FEDs the electron current prescribed by controlled constant current source 301A-301D operably coupled thereto.
Switching circuit 302 is realized by any of many means known to the art such as, for example, mechanical and electronic switching. In some anticipated applications it will be desired that the switching function realized by the switching circuit will be cyclic (periodic recurring) and sequential. Such a switching function, when applied to an image display employing an array of FEDs as described herein, provides for row by row addressing of viewing screen pixels."
From FIG. 3 the amount of time in which each FED element is activated is typically the amount of time for each scan cycle t.sub.f 510 divided by the number of scan lines n or rows in FIG. 2 304B. The power consumption of the display element and the activation circuitry 301A-301D, 302, 303, 306, and 310 is linearly proportioned to the amount of time the FED element is activated.